const etr = document.querySelector('.system-etr')
const contents = document.querySelectorAll('.system-content .content')
    etr.addEventListener('click',function(e){
        if(e.target.tagName === 'A') {
            const aAct = document.querySelector('.system-etr .activelly')
            if(aAct){
                aAct.classList.remove('activelly')
            }
            e.target.classList.add('activelly')
            const index = e.target.dataset.index
            console.log(index)
            for(let i = 0; i < contents.length; i++) {
                contents[i].style.display = 'none'
            }
            contents[index].style.display = 'block'
        }
    })